Diffuser



Nov. `26, 1957 Filed Nov. 7, 1952 J.- R. BOYD DIFFUSER 4 Sheets-Sheet l JCI-1 N F?. BOYD IN V EN T 0R.

Nv. 26, 19.57 J. R. BOYD 2,814,434

DIFFUSER Filed NOV. 7. 1952 4 Sheets-Sheet 2 `JOHN F2. BOYD INVENolle.

Nov. 26,l 1957 J, R, BOYD 2,814,434

DIFFUSER Filed Nov. 7, 1952 4 sheets-sheet s .JOHN R. Bow/DA E? 8 INVENTOR.

BY d

OVERALL ccnvumzsssop` EFFICIENCY (94,)

Nov. 26, 1957` .1. R. BOYD 2,814,434

DIFFUSER Filed NOV. 7. 1952 4 Sheets-Sheet 4 I DIFFusI-:R HAVING 'u f ONE GROOVE' (DELIvERINc-s 3 psl I EXIT PQESSUIQE) coNvENTIoNAI. DIF-FUSE R (AT 3 Pal EXIT 4 PRESSUQE) o 6 zon 30o 4c o soo con CAPACITY (CUBIC FEET PER MINUTE) E E JOI-IN IQ. BOYD INVENTOR. BY JIw-L 0% DIFFUSER John R. Boyd, Venice, Calif., assiguor to McCulloch Motors Corporation, Los Angeles, Calif., a corporation of Wisconsin Application November 7, 1952, Serial No. 319,304

10 Claims. (Cl. 230-127) My invention relates to new and useful improvements in centrifugal compressors, supercharge'rs, and turbines, and more particularly to the control and stabilization of compressible fluid yflow in the diffusers of such apparatus so as to increase the efficiency thereof.

lt is an object of the invention to provide means for stabilizing and controlling the flow of a compressible fluid in the diffusers of centrifugalvcompressors or turbines so as to increase the efficient flow ranges thereof.

it is another object of my invention to provide curved control groove means in the diffuser walls of centrifugal compressors or turbines for stabilizing both the subsonic and supersonic iow of compressible fluids therein.

It is another object of the invention to provide stepped or offset wall means in diffuser entrance passages for stabilizing the flow of compressible fluids entering the diffuscrs of compressors or turbines.

It is a further object of my invention to provide means for reducing friction losses and shock losses in scrolls of turbines and compressors and for attaining more uniform flow distribution and velocity distribution therein.

The foregoing and other objects and advantages are apparent from the following description taken with the accompanying drawings in which:

Figure l is a cross sectional view of a centrifugal compressor showing details of construction of one form of the present invention.

Figure 2 is a sectional View taken on the line 2-2 of lFigure l, and showing the interior of the diffuser.

Figure 3 is a cross sectional view of a `conventional diffuser.

Figure 4 is a cross sectional view of a diffuser embodying the present invention.

Figure 5 is a sectional View similar to Figure 2, illustrating the subsonic flow of compressible fluid in a diffuser embodying the present invention.

Figure 6 is a cross sectional View, on an enlarged scale, taken approximately on the line 6-6 of Figure 5, showing the flow path of compressible fluid in a diffuser embodying the present invention.

Figure 7 is a sectional view on a reduced scale of the interior of a conventional diffuser, illustrating the formation of shock waves therein at supersonic flow conditions.

Figure 8 is a sectional view similar to Figure 2, illustrating supersonic flow in the diffuser of the present invention, and the position of the stable shock wave formed therein.

Figure 9 is a cross sectional view, on an enlarged scale, taken approximately on the line 9-9 of Figure 8, showing supersonic flow passing through the stable shock wave formed in the diffuser' of the present invention.

Figure l0 is a cross sectional view, on an enlarged scale, taken approximately on the line 10-10 of Figure 8, illustrating the supersonic flow passing through the stable shock wave formed in the entrance passage to the diffuser of the present invention.

scale, of a diffuser embodying another form of the present invention, illustrating supersonic flow passing through the stable shock wave formed therein.

Figure l2 is a graph illustrating a comparison of compressor performance, the comparison being between two compressors which were similar except for the adaptation of the present invention to the diffuser of one compressor.

In the drawings the numeral 10 indicates generally a specific embodiment of the present invention, which comprises a scroll casting 11, a cover plate 12 which together with the casting 11 dene a scroll casing or diffuser 13 and an impeller 14 which operates in a casing formed by portions of the parts 10 and 11. The impeller is retained on the end 15 of shaft 16 by means of screw 17, as shown. The shaft 16 is journaled within bearing housing 18 by means of an anti-friction bearing 19, and is mounted so as to provide a running clearance 20 between the left face 21 of the impeller 14 and the inner wall 22 of the scroll casting 11. The bearing housing itself is axially supported within the central section 23 of scroll casting 11, and is held against the left face 24 thereof by means of screws 25.

The cover plate 12, which is bolted to the scroll casting 11, encloses the impeller blades 26, there being a running clearance 27 between the blades 26 and the inner surface 28 of the cover plate 12. The blades themselves provide rotating passageways through which the compressible fluid passes in flowing from the collector chamber 29 to the entrance passage 30 in the scroll casing.

The entrance passage 30 is defined by interior walls 31 and 32 as shown in Figures l and l0. An offset or stepped wall portion 33 extends from an upstream point 34 adjacent the shallowest portion of the diffuser passage 35 to a downstream point 36 approximately 90 degrees downstream from point 34. A convex wall portion 37 extends between lthe interior wall 31 and the offset wall portion 33. Interior wall 3l, the convex wall portion 37 and the offset wall portion 33 together define a radially varying discharge area 38 for the flow passing through the entrance passage 30.

The diffuser passage or scroll passage 35 is defined by inner wall 39, outer wall 40 and side walls 41 and 42, as shown in Figure l. A contro-l groove or passage 43 is formed in the side wall 41 of the diffuser passage 35, and the groove 43 follows the downstream curvature of passage 35. The diffuser passage 35 is itself curved about the impeller axis, the curvature being such that a radius from the impeller axis to a point on the center line of the diffuser passage continuously increases in magnitude as the point on the center line of the diffuser passage moves downstream. The groove 43 is preferably positioned within the middle third portion of wall 41, lying between walls 39 and 40. As shown in cross-section in Figure 1, the groove walls are continuously curved, with two convex edge or side walls 44 curving outwardly from scroll wall 41 to meet side walls 45, which themselves join concave inner or bottom wall 46 of groove 43. The groove eX- tends from an upstream point 47 near the downstream end 36 of offset wall portion 33 to a downstream point 48 near the downstream end of the volute shaped scroll passage 35. In Figure 4 the groove passage 43 is sho-wn positioned in the curved side wall 49 of a conventional curved-wall diffuser 50.

At subsonic flow conditions, the flow leaves the rotating impeller 14, flows through the entrance passage 30, and enters the diffuser passage 35. The mean flow path of the gases flowing at subsonic velocities tends to follow a helical or spiral course 51 in a conventional diffuser 50 as shown in Figure 3. The energy losses of the gases,

- FigureV l1 is a cross sectional view, on an enlarged l which .are due to friction :and which are evidenced as loss Patented Nov. 26, 1957v of pressure head, are functionally proportional to the total length of the mean flow path followed by the gases in the scroll. This means that the energy losses of the gases would tend` to beA reduced by reducing or `eliminating the spiral flow of the gases as they flow downstream in the scroll passage 33'.

The present invention tends to prevent spiral rotation of the gases as they fiow downstream in the diffuser passage 35 at subsonic velocities, and consequently to minimize energy losses resulting therefrom. Groove passage 43 is positioned in the curved Wall 49 of Ithe diffuser 50 shown in Figure 4, and in the wall 41 of diffuser 13 shown in Figures l, 6, 9 and `l0, and as a result the spiral or rotational flow ofthe gases in these diffusers is minimized, with consequent increase in pressure head` developed. Itis believed that the `boundary layer gases on either side ofy the groove passage 43 tend to flow over the convex side walls 44 and into the groove passage 43, creating low pressure areas 52 adjacent the convex side walls 44. The gases within the diffuser passage 35 tend to flow toward the low pressure areas 52 `adjacent the convex side Walls` 44 as shown in =Figure 6, establishing fiow paths inconsistent with' spiral or helical rotation in the diffuser passage 35. The gases that flow into the groove passage 43 flow downstream. The groove structure there fore racts asa ow control or stabilizer permitting the `gases to diffuse uniformly, with greatly reduced rotation, in directions having downstream components and also components directed toward the diffuser wall containing the groove structure. The beneficial results obtained by the introduction of this groove structure in diffuser walls consist in a reduction in frictiona'l losses undergone by the gases and increased overall compressor efficiencies at subsonic gas velocities.

At high impeller speeds, the tangential velocity 53 of the gases flowing from the impeller 14 is increased, and the resultant exit velocity 54 of the flow becomes supersonic, as illustrated in Figure 7. As the supersonic ow enters a conventional `diffuser passage 64, it passes through a series of shock waves S which stand out from the dif fuscr walls throughout the diffuser passage 64. As the supersonic fiow .passes through these shock waves 55, it undergoes an increase in pressure and a decrease in velocity, the gain in pressure differing from the theoretical gain by an amount equal to shock losses. These `shock losses are evidenced by a rise in temperature of the ow. As a result of the pressure rise through the shock waves 55, a net pressure difference results andthis pressure difference acting on each shock wav-e tends to move it around within the diffuser `passage 64, resulting in shock wave mobility. As a result in a conventional diffuser the shock waves are dynamically unstable under supersonic flow conditions. Shock wave instability and mobility result in `general ow instability of the gases, which in turn results in increased friction losses and decreased overall efficiency of the compressor.

The present invention overcomes shock wave instability and energy losses resulting therefrom by providing a dif- -fuser passage in which a control groove is positioned in a wall thereof. illustrated in Figure 9, 4a control groove 43, as described supra, is positioned in the dif-` fuser wall 41, and under supersonic flow conditions a strong, stable shock wave 56 forms in the diffuser passage `35. The end of this shock wave is tied down or affixed to the groove passage 43, by virtue of its surface irregularity. lt is not proposed to describe the physical phenomena associated with the formation and nature of such shock waves, as such phenomena forma part ofesupersoni-c theory. Suffice itA to say, however, that a stable shock Wave 56 does form and projects outwardly -romrgroove passage 43in a direction almost paralleling diffuser walls 39 and 40. The presence of the` groove passage `43 in wall 41Y of the diffuser results in the formation of `this `particular shoclr-.waveSG which has the properties op stability .and advantageons` location and direction fin the diffuser passage 35. The shock wave 56 presents a slightly concave sheet-like surface 57 to the supersonic ow inpinging upon it. The shock Wave 56 assumes the downstream curvature of the diffuser passage 35, since it is seemingly attached to the groove passage 43.

As the supersonic ow passes through the shock wave 56 it undergoes an increasein pressure and temperature, and is reduced to subsonic velocity in the region 58 of the scroll or diffuser which lies radially outward from the shock wave 5'6. Since the flow is subsonic in region 58, no shock waves can form on the wall 4f) of the scroll, and the high static pressure flow is confined between shock S6 and wall 40 where it continues to diffuse as it ows downstream. It is thus seen that as a result of introducing groove 43 in wall 41 of the scroll, the flow is effectively stabilized, being confined to the outer portion 58 of the scroll passage 35 where it flows downstream at subsonic velocities and increased pressures.

ln the upstream portions of the diffuser passage 3S between points 34. and 36, the convex wall portion 37 joins interior wall 31 with stepped, or offset wall 33. As the supersonic flow emerges from the impeller, it flows through the entrance passage 39 defined by walls 3]., 32, 33 and 37, anda stable shock wave 59 forms in the entrance passage 30 with its end seemingly tied down to the convex wall. portion 37. The shock wave 59 ex* tends across the entrance passage 30, and as the supersonic flow passes through the shock its velocity drops to su'bsonic levels, whereby the formation of shock waves on the walls ofthe comparatively shallow upstream end of the diffuser passage 3S is prevented. The shock wave 59 formed in the entrance passage 36 serves the same purpose 4in the shallow upstream end of the diffuser passage 3f) as does the shock wave 56 in other portions of `the diffuser passage.

The shock wave 59 remains relatively fixed at all irnpeller speedspro'ducing supersonic gas flow, and as a resul-t shock losses are reduced at supersonic flow conditions in the Vvscroll passage 35.

lnFigure ll there, is shown another form of the present invention. A second control groove 60 is introduced into the scroll passage 35, and is located in wall 61 opposite from groove 43. This second groove is similar in structure to groove 43, and its location in wall 61 is related to the dimensions of the diffuser and impeller and the range of impeller speeds over which the supercharger or turbine will be operated. Groove 60 is positioned in wall 61with respect to groove 43 so as to maximize the efficiency of a particular supercharger or turbine over the desired' impeller speed range. In Figure ll the groove 60 is positionedin wall 61 relatively oppositely from groove y43l and extendsaround the scroll passage 35 to points opposite` the upstream and downstream limits of groove 43. When the flow becomes supersonic, a shock wave 62 forms in the scroll passage 35 between grooves 43 and 60. The ends of the shock Wave are effectively tied down to the two grooves so that the shock wave is stabilized and presents a concave sheet-like surface 63 tothe impinging supersonic flow. As the ow passes through the shock, it undergoes an increase in pressure and temperature, and emerges from the stabilized shock wave at decreased velocity and increased pressure, which of course isA somewhat less than the highest pressure attained inpassing through the shock wave 62. As the high pressure gas flows downstream in the scroll passage 35 `at subsonic velocities, it is confined within region 58 of the scroll passage 35, bounded by the three walls 41, 40,`

61 and 'theshockwave 62. The effective position of the shock wave -62 which determines the cross sectional area ofl regionV 53' of the scroll passage is itself determined bythe location-ofthe two grooves 43 and 60 formed within-,scroll wallsf41 and,61. The crosssectional area of the region 58of the scroll `passage bears a relation to the overall efficiency of the scroll atsupersonic flow conditions, so thatcontrol of the efficiency of the scroll and '5 supercharger is related to the control of the cross sectional area of region 58 of the scroll passage and this area is effectively controlled by the existence and position of the shock wave 62, which is in turn determined by the relative positions of grooves 43 and 60. The grooves 43 and 60 cause the formation of the stable shock wave 62 which is stabilized at supersonic flow velocities. The grooves 43 and 60 position the shock wave by locating, or tying-down the ends of the wave. The relative positions of grooves 43 and 60 determine the position of the shock wave 62 in the scroll passage 35, and the two grooves may be located so that scroll eiciency, which is related to shock wave stability and location, is maximized.

In Figure 12 two experimental supercharger efficiency curves are plotted against iiow rates. As shown in the graph, the eiciency curve for a supercharger having a diffuser without the present invention adapted thereto and delivering 3 pounds per square inch pressure peaks rather sharply at a delivery rate between 250 and 350 cubic feet per minute, to attain a maximum eiiciency of 72%. The eiciency curve for the same supercharger having a control groove in its diffuser passage and delivering the same pressure increases rapidly to attain 72% eiiciency at 200 cubic feet per minute ow rate, and thereafter increases to attain 76% eiciency at 300 cubic feet per minute flow rate. The overall efciency of the supercharger having the control groove in its scroll passage does not drop below 72% yeii'iciency until the ow rate exceeds 400 cubic feet per minute. Moreover, at ow rates equal to 50 and 550 cubic feet per minute, the overall efficiency has been approximately doubled. It is seen that the introduction of the control groove in a diffuser wall of the supercharger results in greatly increased overall eiiiciency at both subsonic and supersonic ow conditions, whereby the elcient ilow range of the supercharger is markedly increased.

While the embodiment of the present invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

I claim:

1. A compressor assembly comprising: a casing; an impeller mounted for rotation within said casing; curved wall means defining a volute shaped diffuser passage for the flow from said impeller, said curved wall means including an outer wall and side walls joined to said outer wall and extending inwardly from said outer wall toward said impeller; each of said side walls being provided with curved control groove means; said curved control -groove means having walls defining a control passage having a lirst portion removed from said diffuser passage and a second portion communicating with that portion of the diffuser passage adjacent to the side wall.

2. In a diffuser for a centrifugal compressor having a casing with a central inlet and a peripheral outlet, a rotor in said casing having fluid passages communicating with said inlet and discharging at the peripheral surface of said rotor, said diffuser comprising a scroll diffuser chamber connected to said casing about said rotor, said chamber being formed by an outer wall and side walls extending from said outer wall toward the periphery of said rotor, Wall means depending from said side walls toward said rotor and forming an entrance passage for ilow of fluid from said rotor to said scroll diffuser chamber, a control groove in the inner surface of one of said side walls, said control groove being curved and extending toward said outlet and having end portions which lie on opposite sides of the rotor axis, said control groove being narrower than the width of the side wall in which it is located.

3. In a diifuser for a centrifugal compressor having a casing with a central inlet and a peripheral outlet, a rotor in said casing having uid passages communicating with said inlet and discharging at the peripheral surface of said rotor, said diffuser comprising a scroll diffuser 6 chamber connected to said casing about said rotor, said chamber being formed by an outer wall and side walls extending from said outer wall toward the periphery of said rotor, wall means depending from said side Walls toward said rotor and forming an entrance passage for flow of fluid from said rotor to said scroll diffuser chamber, a control groove in the inner surface of one of said side walls, said control groove being curved and extending toward said outlet and having end portions which lie on opposite sides of the rotor axis, said control groove being narrower than, and having edges spaced from the inner and outer edges of, said side wall in which it is located.

4. In a diffuser for a centrifugal compressor having a casing with a central inlet and a peripheral outlet, a rotor in said casing having fluid passages communicating with said inlet and discharging at the peripheral surface of said rotor, said diffuser comprising a scroll diffuser chamber connected to said casing about said rotor, said chamber being formed by an outer wall and side walls extending from said outer wall toward the periphery of said rotor, wall means depending from said side walls toward said rotor and forming an entrance passage for tiow of fluid from said rotor to said scroll diffuser chamber, a control groove in the inner surface of one of said side walls, said control groove being curved and extending toward said outlet and having end portions which lie on opposite sides of the rotor axis, said control groove being narrower than the width of the side wall in which it is located, having a concavely curved bottom wall and convexly curved edge walls connecting the bottom wall with the contiguous portions of the side wall in which the control groove is located.

5. In a diffuser for a centrifugal compressor having a casing with a central inl-et and a peripheral outlet, a rotor in said casing having fluid passages communicating with said inlet .and discharging at the peripheral surface of said rotor, said diffuser comprising a scroll diffuser chamber connected to said casing about said rotor, said chamber being formed by an outer wall and side walls extending from said outer wall toward the periphery of said rotor, Wall means depending from said side walls toward said rotor and forming an entrance passage for flow of fluid from said rotor to said scroll diiuser chamber, a control groove in the inner surface of one of said side walls, said control groove being curved and extending toward said outlet and having end portions which lie on opposite sides of the rotor axis, said control groove being narrower than, and having edges spaced from the inner and outer edges of, said side wall in which it is located, having a concavely curved bottom wall and convexly curved edge walls connecting the bottom wall with the contiguous portions of the side wall in which the control groove is located.

6. In a diffuser for a centrifugal compressor having a casing with a central inlet and a peripheral outlet, a rotor in said casing having fluid passages communicating with said inlet and discharging at the peripheral surface of said rotor, said diffuser comprising a scroll diffuser chamber connected to said casing about said rotor, said chamber being formed by an outer wall and side walls extending from said outer wall toward the periphery of said rotor, Wall means depending from said side walls toward said rotor and forming an entrance passage for ilow `of fluid from 4said rotor to said scroll diffuser chamber, la control groove in the inner surface of one of said side walls, said control groove being curved and extending downstream of said diffuser chamber, said control groove being narrower than, and having edges spaced from the inner and outer edges of, said side wall in which it is located.

7. In .a diffuser for a centrifugal compressor having a casing with a central inlet and a peripheral outlet, a rotor in said casing having fluid passages communicating with said inlet and discharging -at lthe peripheral surface of said rotor, said diffuser comprising a scroll diluser chamber connected to said casing about said rotor, said cham ber being formed by an outer wall and `side walls extending from said outer wall toward the periphery of said rotor, ythere being wall means at `the inner edges of said side walls connecting said side walls to said casing, a control groove in the inner surface of `one of said side walls, said control groove being curved .and extending toward said outlet and having end portions which lie on opposite sides of the rotor axis, said control groove being narrower than the width of the side wall in which it is located.

8. In a diffuser for a centrifugal compressor having a casing with a central inlet and a peripheral outlet, a rotor in said casing having Huid passages communicating with said inlet and discharging at the peripheral surface of said rotor, said diffuser comprising a scroll diifuser chamber connected lto said casing about said rotor, said chamber being formed by an outer wall and side walls extending from saidfouter Wall toward the periphery of said rotor, there being wall means at the inner edges of said side walls connecting said side walls to said casing, a control groove in the inner surface of one of said side walls, said control groove being curved and extending toward said 'outlet and having end portions which lie on opposite sides of the rotor axis, said control groove being narrower than the width of the side wall in which it is located, having a concavely curved bottom wall and convexly curved edge walls connecting the bottom Wall with the contiguous portions of the side wall in which the control groove is located.

9. In a diiuser for a centrifugal compressor having a casing with a central inlet and a peripheral outlet, a rotor in said casing having uid passages communicating with said inlet and discharging at the peripheral surface of said rotor, said diffuser comprising a scroll diffuser chamber connected to said casing about said rotor, said chamber being formed by an outer wall and side walls extending toward the periphery of said rotor, means for controlling the flow in said diffuser chamber, said means comprising a curved wall extending along one of said side walls for forming a control groove for causing the formation of a shock wave extending across said diffuser passage, said curved wall being narrower than, and having its edges spaced from the edges of, the side wall along which it extends, the ends of said control groove lying on opposite sides of the axis of said rotation of the compressor.

10. In a diffuser for a centrifugal compressor having a casing with a central inlet and a peripheral outlet, a rotor in said casing having fluid passages communicating with said inlet and discharging at the peripheral surface of said rotor, said diffuser comprising a scroll diluser chamber connected to said casing about said rotor, said chamber being formed by an outer Wall and side walls extending toward the periphery of said rotor, means for controlling rthe iiow in said diiuser chamber, said means comprising a curved wall extending along one of said side Walls for forming a control groove for causing the formation of a shock wave extending across said diffuser passage, said curved wall being narrower than, and hav ing its edges spaced from the edges of, the side wall along Which it extends, said curved wall providing for the groove 4a bottom wall which is concavely curved laterally thereof and edge walls for the groove convexly curved transversely thereof.

References Cited in the file of this patent UNITED STATES PATENTS 1,462,592 Bentley July 24, 1923 1,998,778 Gregg Apr. 23, 1935 2,160,666 McMahan May 30, 1939 2,377,740 Alford June 5, 1945 2,471,174 Trumpler May 24, 1949 FOREIGN PATENTS.

71,172 Austria Feb. 10, 1916 235,397 Germany June 12, 1911 554,166 Great Britain June 23, 1943 724,553 Germany Aug. 29, 1942 

